According to his LinkedIn profile, Mr Birthisel, a former Rio Tino employee, has worked in South East Asia since 2003.

His most recent position is listed as vice president at Asia Mangan Grup, an Indonesian-based manganese mining company founded in 2011.

He worked as a Rio Tinto safety and training adviser in Western Australia, from 2000-2002.

Sun Star Cebu reports Mr Birthisel and his girlfriend allegedly lured the women with promises of waitressing and housekeeping work in Australia.

Mr Birthisel claims his girlfriend and her friends were travelling to Singapore for a job interview, and he was travelling with them to ensure their safety.

The Philippines' National Bureau of Investigation alleges Mr Birthisel and his girlfriend were "recruiting, transporting and hiring women through use of fraud under the pretext of overseas employment for the purpose of exploitation".

Convicted human traffickers in the Philippines face life imprisonment, while attempted human traffickers can face sentences of up to 15 years in jail.